The present invention relates to a stain-free fixing device for use in an electrophotographic printer.
Nowadays, high-speed electrophotographic printers are becoming common. The high-speed printing, however, increases the speed of consumption of toner and paper which incessantly stains the glass window of a fixing device with dispersed unfixed toner. The incessant staining overtakes regular maintenance services. Therefore, the industry strongly depends on maintenance-free fixing devices so as to reduce the maintenance toil and cost.
In order to prevent the staining of glass windows in the electrophotography, the following methods have been proposed:
1) A method of removing air containing unfixed toner by suction through a sucking device; PA1 2) A method of enabling unfixed toner to repel the glass window by applying direct current (DC) voltage to two electrodes embedded in the glass window so that the surface of the glass window facing the paper is charged with electric charge equal in polarity to the electric charge of the toner (Japanese Patent Application Laid-Open No. 2-272593 (1990)). PA1 3) A method of enabling unfixed toner to repel the glass window by disposing a trigger electrode closest to the glass window and charging the surface of the glass window facing the paper with equal polarity to the polarity of the toner (Japanese Patent Application Laid-Open No. 7-13457 (1995)).
However, method 1) is not effective to remove unfixed toner with suction only, because of the short distance between the paper and glass face, thus necessitating the continued cleaning of the glass window.
The method 2) requires the provision of a special glass window allowing an electrode to be embedded therein, and an extra power source for impressing direct current (DC) voltage across the electrode, thereby increasing the production cost and a complicating the maintenance.
The method 3) encounters a problem that the toner repelling force is weakened in the course of using the fixing device, owing to the fact that the flash lamp thermally affects the trigger electrodes. In addition, because of the high tension applied to them, the trigger electrodes themselves generate a large amount of heat. In this way, the trigger electrodes tend to deform or crook due to heat over a long period of use. The deformation causes the trigger electrodes to displace, even partially, in a longitudinal direction from the original position adequately set with respect to the glass window. Thus, the method 3) does not provide a solution to the frequent maintenance, because the heat involved in this method requires regular maintenance when the fixing device is used for a long time.